The principal objectives of the proposed research program are: (a) to gain a basic knowledge of the fundamental processes of maturation, reproduction and aging in filarial worms which parasitize in man in order that we might understand more clearly and interpret more accurately the clinical manifestations of bancroftian and malayan filariasis. To achieve these goals, the filaria, Brugia malayi, shared by man and primates is being used as the principal model for laboratory study. Through the long-term study of experimental infections produced with known numbers of worms it will be possible to make a firm assessment of the reproductive potential of the female worm, the relationship between worm burden and levels of microfilaremia and the longevity of the adult worms, and (b) to clarify the relationships of Dipetalonema perstand of man to the perstans-like filariae of primates. Efforts will be made to clarify taxonomic relationships of these species, to describe their morphology, distribution and habitats in the definitive hosts, their behavior and their role as pathogens using naturally and experimentally-infected monkeys and apes as laboratory models.